Optical fibers have advantages such as a wide transmission frequency band, large capacity, low consumption and good capability of resisting interference. Therefore, they are suitable to be used as transmission media of high-speed and wideband services. In various optical access technologies, the passive optical network (PON), which is currently in use, is drawing wide attention.
The PON technology is a point to multi-point (P2MP) optical access technology, including an optical line terminal (OLT), an optical splitter, optical network units (ONUs)/optical network terminals (ONTs) and optical fibers connecting these devices. The OLT, as an office-end device, is connected with the optical splitter by using a backbone optical fiber, and the optical splitter is connected to each ONU by using a separate branch optical fiber. The optical splitter implements the optical splitting function in the downlink direction to send downlink optical signals of the OLT to all the ONUs by using the branch optical fibers, and implements the optical signal aggregation function in the uplink direction to aggregate optical signals sent from all the ONUs and send the aggregated signals to the OLT by using the backbone optical fiber. To prevent the collision of uplink data sent from each ONU in the uplink direction, the OLT must measure the distance of each ONU to control the time and the duration when and during which each ONU occupies an uplink optical fiber, and meanwhile, each ONU is required to send the uplink data by using the burst time division multiple access (TDMA) multiplexing.
To support the long reach data transmission between the OLT and the ONUs, the optical signals in the optical fibers need to be amplified, and thus a long reach PON (LR-PON) is derived. As illustrated in FIG. 1, an optical amplifier (OA) or an optical-electrical-optical (OEO) converter is added in the optical transmission channel. In general, the optical splitter and the OA/OEO converter may be integrated in a same device, called an extender box (EB). The topology between the EB and the ONUs is P2MP, so it is the topology between the OLT and the ONUs.
Generally, a distributed base station (BS) includes a radio remote unit (RRU) and a baseband unit (BBU). The RRU is usually placed indoors, so the home BS is usually the RRU of the BS. The RRU and the BBU are connected with each other by using a private optical interface through an uplink optical fiber and a downlink optical fiber. The private optical interface cannot form the industrial scale effect, thus having high costs. When the standardized PON is used as a normalized interface between the RRU and the BBU of the BS, because the PON adopts the single-fiber bidirectional technology, a duplexer or a wavelength division multiplexing (WDM) module needs to be added in the RRU and the BBU to support the single-fiber bidirectional technology of the PON. The duplexer is high in costs, while, in general, only the RRU of the home BS with low costs is acceptable to users. How to use the standardized PON as the interface between the RRU and the BBU and how to control the costs of the home BS to a smaller range become critical problems.
In addition, when used as the backhaul of the BS, the PON is a transmission technology instead of a simple access technology, so the system security requirement of the PON is much higher than that of the PON used as a simple access technology. Operators especially require that the PON system should be able to resist the abnormal luminescence of ONU devices, which is actually a denial of service (DoS) damaging the connection of the physical layer.
In normal circumstances, each ONU sends data by occupying an uplink channel according to the authorization of the OLT, so that the signal collision of the network will not occur. However, when the ONU devices randomly or permanently occupy the uplink channels because of faults and not responding to the authorization of the OLT, or when some malicious ONUs freely occupy the uplink channels, the PON will be in a state of paralysis, thus affecting the normal working of the 802.16 BS. It is impossible to locate the faulty ONU devices due to the passive characteristics of branch nodes. When used as the backhaul of the BS, the PON is required to resist the abnormal luminescence of the ONU devices, and this security requirement is a critical technical problem to be solved.